New device achieves self-biased solar hydrogen generation through microbial electrohydrogenesis at lab scale

Oct 10, 2013

A novel device that uses only sunlight and wastewater to produce hydrogen gas could provide a sustainable energy source while improving the efficiency of wastewater treatment.

A research team led by Yat Li, associate professor of chemistry at the University of California, Santa Cruz, developed the solar-microbial device and reported their results in a paper published in the American Chemical Society journal ACS Nano. The hybrid device combines a microbial fuel cell (MFC) and a type of solar cell called a photoelectrochemical cell (PEC). In the MFC component, bacteria degrade organic matter in the wastewater, generating electricity in the process. The biologically generated electricity is delivered to the PEC component to assist the solar-powered splitting of water (electrolysis) that generates hydrogen and oxygen.

Either a PEC or MFC device can be used alone to produce . Both, however, require a small additional voltage (an "external bias") to overcome the thermodynamic barrier for proton reduction into hydrogen gas. The need to incorporate an additional electric power element adds significantly to the cost and complication of these types of energy conversion devices, especially at large scales. In comparison, Li's hybrid solar-microbial device is self-driven and self-sustained, because the combined energy from the organic matter (harvested by the MFC) and sunlight (captured by the PEC) is sufficient to drive electrolysis of water.

In effect, the MFC component can be regarded as a self-sustained "bio-battery" that provides extra voltage and energy to the PEC for hydrogen gas generation. "The only energy sources are wastewater and sunlight," Li said. "The successful demonstration of such a self-biased, sustainable microbial device for hydrogen generation could provide a new solution that can simultaneously address the need for and the increasing demand for clean energy."

Microbial fuel cells rely on unusual bacteria, known as electrogenic bacteria, that are able to generate electricity by transferring metabolically-generated electrons across their cell membranes to an external electrode. Li's group collaborated with researchers at Lawrence Livermore National Laboratory (LLNL) who have been studying electrogenic bacteria and working to enhance MFC performance. Initial "proof-of-concept" tests of the solar-microbial (PEC-MFC) device used a well-studied strain of electrogenic bacteria grown in the lab on artificial growth medium. Subsequent tests used untreated municipal wastewater from the Livermore Water Reclamation Plant. The wastewater contained both rich organic nutrients and a diverse mix of microbes that feed on those nutrients, including naturally occurring strains of electrogenic bacteria.

When fed with wastewater and illuminated in a solar simulator, the PEC-MFC device showed continuous production of hydrogen gas at an average rate of 0.05 m3/day, according to LLNL researcher and coauthor Fang Qian. At the same time, the turbid black wastewater became clearer. The soluble chemical oxygen demand—a measure of the amount of organic compounds in water, widely used as a water quality test—declined by 67 percent over 48 hours.

The researchers also noted that declined over time as the bacteria used up the organic matter in the wastewater. Replenishment of the wastewater in each feeding cycle led to complete restoration of electric current generation and hydrogen gas production.

Qian said the researchers are optimistic about the commercial potential for their invention. Currently they are planning to scale up the small laboratory device to make a larger 40-liter prototype continuously fed with . If results from the 40-liter prototype are promising, they will test the device on site at the wastewater treatment plant.

"The MFC will be integrated with the existing pipelines of the plant for continuous feeding, and the PEC will be set up outdoors to receive natural solar illumination," Qian said.

"Fortunately, the Golden State is blessed with abundant sunlight that can be used for the field test," Li added.

Explore further: Researchers take big-data approach to estimate range of electric vehicles

Related Stories

Microbes strip power from poo

Sep 17, 2013

EPSRC-funded scientists have developed a process using microbes which removes the need to use electricity to process sewage at treatment plants. The microbes can also be used to produce large quantities of ...

Bacteria -- energy producers of the future? (w/ video)

Aug 22, 2011

All of us use water and in the process, a lot of it goes to waste. Whether it goes down drains, sewers or toilets, much of it ends up at a wastewater treatment plant where it undergoes rigorous cleaning before it flows back ...

HyperSolar shows dirty water no barrier to power world

May 24, 2012

(Phys.org) -- The Santa Barbara, California, company, HyperSolar, is set to transparently share the ups and downs of its research experiences toward the company’s ultimate vision, successfully producing ...

Recommended for you

First-of-a-kind supercritical CO2 turbine

Oct 20, 2014

Toshiba Corporation today announced that it will supply a first-of-a-kind supercritical CO2 turbine to a demonstration plant being built in Texas, USA. The plant will be developed by NET Power, LLC, a U.S. venture, together w ...

Drive system saves space and weight in electric cars

Oct 17, 2014

Siemens has developed a solution for integrating an electric car's motor and inverter in a single housing. Until now, the motor and the inverter, which converts the battery's direct current into alternating ...

Dispelling a misconception about Mg-ion batteries

Oct 16, 2014

Lithium (Li)-ion batteries serve us well, powering our laptops, tablets, cell phones and a host of other gadgets and devices. However, for future automotive applications, we will need rechargeable batteries ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Telekinetic
3 / 5 (4) Oct 10, 2013
I'm all for this remarkable and "green" breakthrough. If given funding it could make a dent. While they're at it, it would behoove energy companies to make use of methane from livestock waste and human sewage like they do overseas. But then you might be stepping on some toes if it affects the price of oil and gasoline which it would. Maybe WikiLeaks will publish a document revealing collusion between Big Oil and our government, causing a scandal that will last until you need to fill your tank again.